Toddlerhood is an ideal period for health promotion/obesity prevention. Not only are diet and physical activity habits established during toddlerhood, but toddlers in low-income families are disproportionately affected by the obesity epidemic. The home environment can either facilitate or inhibit healthful eating and physical activity. For toddlers, the social and physical environment within a household is largely dependent on the caregiver. Identifying an innovative method for examining social and physical factors in the home environment that are related to health behaviors among very young children would enable researchers to identify context-specific health-promotion interventions. Ecological Momentary Assessment (EMA) is a method of real-time data collection that allows participants to report on behaviors and factors that influence behaviors, in real-time, at multiple time points, in their own environment. We have demonstrated the feasibility and validity of using EMA to measure toddler physical activity and diet. The purpose of this proposed project is to use EMA to determine social and physical factors in the home environment associated with toddler diet and physical activity following the Conceptual Model for Eating and Physical Activity Environmental Influences in the Home. This study has two specific aims. The first is to identify factors in the home environment that are associated with toddler physical activity by comparing mother's real-time report of aspects of/events in the home environment collected via EMA to toddler physical activity collected using three approaches: (1) the mother's report of real-time physical activity collected simultaneously via EMA, (2) time-stamped accelerometer-measured physical activity, and (3) daily minutes in moderate-vigorous physical activity collected via accelerometry (over >5 consecutive days). The second aim is to identify factors in the home environment that are associated with toddler diet by comparing mother's real- time report of aspects/events in the home environment collected via EMA to diet collected using two approaches: (1) mother's report of real-time food consumption collected simultaneously via EMA and (2) overall estimate of daily food consumption via 24 hour dietary recall data. The overall goal of this project is to identify health promotion/ obesity prevention intervention areas in the home environment. Following this R03, an R01 application will propose the development, pilot-testing, and efficacy trial of an ecological momentary intervention to improve toddler diet and physical activity by encouraging changes specific to the family's home environment.